Refractory metal composition



Patented Feb. 27, 1945 2,370,242 Fl C E 2,370,242 REFRACTORY METALCOMPOSITION Franz R. Hensel and Ea R Mallory & dianapolis, Ind., acorporation of lnd., asslgnors to P.

rl I. Larsen, Indianapolis,

00., Inc., In- Delaware No Drawing. Application January 15, 1943,

Serial No. 472,482

V 4 Claims. (Cl. 75-22) This invention relates to metal compositions (b)Molybdenum particles coated with rhoand articles made therefrom. dium 60An object is to improve metal powder'compo- Silver 40 sitions. r

Another object of the invention is to improve 5 g gfg particles matedwith 65 powder metal bodies such as electric contacts,

Silver 35 welding electrodes, welding dies, current carrying hearings orbushings, valve seats and the like. ((1) u l sten pa s Coa ed w th rho-Other objects of the invention will be apparent d1l1m 50 from thedescription and claims. 10 S11v6! 50 The present invention contemplatesa metal (e) Tungsten coated with rhodium 80 composition made fromrefractory metal powsilver 2o ders, particularly tungsten andmolybdenum, which are individually coated with protective MolybdenumParticles coated with i layers of a palladium-platinum group metal such15 and/Or panadhlm 50 as platinum, palladium or rhodium and are S11v9!bonded together in a metal composition with a (g) M l bd n articlescoated with platimetal from the first group of the periodic table nu andor palladium 60 such as copper, silver or gold. silver 40 33 525,222 :3253 3 525 232 (h) Tungsten particles coated with platinum coating and thecoating of protective metal such palladium as platinum, palladium orrhodium may vary ver '7 in thickness from a fraction of a micron to sev-(i) Tungsten particles coated with platinum eral thousandths of an inch.Thus the relative and/or palladium 50 percentages of refractory metal orcompound and Silver 50 protective metals in the coated powders used forproducing the metal composition of the present (7) gg i gfi i withplatinum and/or 3 invention may fall within the following range Silver20 of proportions: so

p t; (0) Tungsten coated with platinum and/or I Refractory metal 99,99 t10 palladium or rhodium 45 Palladium-platinum group metal 0,01 t 90 Gold55 The coated powders are interspersed and w Tun sten co t d with plinum bonded with the second group metal and th r palladmm or rhod1um 70suiting compositions may fall within the follow- Copper 30 mg range: pt; (or) Tungsten coated with platinum and/or Coated tungsten ormolybdenum powpalladium or rhodium 50 ders 51,0 99 4 Copper 50 Coppersilver or Balance The protective coating of rhodium, platinum This rangemay be divid d t t genera] or palladium may be applied by any one ofseveral classes of.materia1s, namely: methods such as electroplating,cathode sputtering; metal spraying, condensing evaporated g gfrefractory compositlons contam' metal on the particle surfaces, chemicaldeposi- Percent tion. They may also be coated by first coating c trefracmr powders 5013399 the powders with a dispersible adhesive. thenCopper silver or g ld Balance dust ng the adhesive Coated particles theP d 1 n i t t l protective metal in powder form and subseg 0m g me mg nme a compo quently heating the coated powders to'disperse 5 con a ngPercent the adhesive and diffusing the protective metal onto thesurfaces of the refractory powders." It Coated refractory puwders 5 tois'also possible to use a metal paste as a'coating Copper, silver orgold Balance medium. a Following are several examples of suitable 55 Themetal-compositions of thepresent invenmetal compositions: tion may bemade from the coated particles in Percent several ways. The coatedrefractory particles, I (a) Molybedenum particles coated with rhoor amixture of them, may be pressed to form a dium 50 powder compact and thecompact then sintered Silver 50 6 at a suitable temperature such as 1200C. to form the mixture.

a slnter-bonded metal body. This body is then impregnated with silver,copper or gold or any alloy of two or more Of these, by placing thefirst group metal in contact with the sintered compact and heating theassembly in a reducing atmosphere to a, temperature above the meltingpoint of the lower melting metal so that it will flow into the pores ofthe sintered body and fill them.

The metal composition may also be produced by mixing the coatedparticles directly with powders of copper, silver or gold, or mixturesof these, pressing the mixed powders and then sintering the pressedmixture at a suitable temperature such as 950 C. to produce the finishedcomposition. If desired, subsequent repressing or coining operations maybe applied to further increase the density and improve the physicalcharacteristics of, the composition.

A third method of manufacture comprises a combination of the above twomethods. According to this method, a portion of the copper, silver orgold in the form of a powder is mixed with the coated refractory powdersand the mixture pressed in a suitable die. The pressed body is thensintered at a temperature to cause binding, such as 1250 C. Additionalamounts of copper, silver or gold are then placed in contact with thesintered body and the assembly heated to a temperature above the lowermelting point metal to cause impregnation.

During the sintering operation, according to any of the above methods,the protective layers oi platinum, palladium or rhodium on therefractory metal particles difiuse into the refractory material to agreater or lesser extent, forming alloys or compositions at the surfacesof the particles. These surface layers are considerably more noble incharacter as far as oxidation is concerned than the refractory particlesthemselves. The degree of diffusion of the protective metal will dependupon the time and temperature of the sintering process. It is alsocontemplated that in some cases the coated powders .may be pre-sinteredin the loose state to accomplish diffusion before the powders are usedin manufacturing the metal composition.

An advantage of the present composition and process resides in theafilnity between the first group metals such as copper, silver and goldand the protective metals such as palladium, platinum or rhodium. Sincethe first group metals have a tendency to alloy with the protectivelayers they are readily drawn into any pores or spaces in the metalcompact resulting in a denser and more nearly perfect and homogeneousmetal structure. The alloying also produces a strong bond between thevarious metal phases present.

In some cases additions of small proportions of other ingredients may bemade to the compositions. For instance, from a fraction of a per cent toof carbon or boron may be added to The carbon is preferably in the formoi graphite.

Such elements as nickel, cobalt, iron, manganese or silicon may be addedin proportions ranging from a fraction of 1% to 30%. These have theefiect of increasing the hardness, wear resistance and tensile strengthof the compositions.

One important use of the metal compositions of the present invention isin electric contacts. Electric contacts have heretofore been produced ofcompositions of refractory metals and compounds with silver and copperin various proportions. However, such compositions have developedrelatively high contact resistances between the contacting surfaces andhave exhibited a substantial temperature rise when subjected tocontinuous operation. The use of a protective metal coating from thepalladium-platinum group on the refractory particles reduces the contactresistance considerably and produces a contact much less subject tooverheating.

By using contacts formed of the compositions described on one or bothsides of a contact pair, sticking and high contact resistance can beeliminated in most cases.

Refractory compositions of the present invention which are particularlysuitable for cooperation with cadmium oxide contacts of the typedescribed in l-lensel Patent 2,145,690 are coated molybdenum particleswith silver, and coated tungsten with silver.

While specific embodiments of the invention have been described, it isintended to cover the invention broadly within the spirit and scope ofthe appended claims.

What is claimed is:

l. A metal composition formed of particles of refractory metal selectedfrom the group consisting of tungsten and molybdenum, and a coatingthereon of metal selected from the group consisting of palladium,platinum and rhodium and metal selected from the first group of thePeriodic Table consisting of copper, silver and gold interspersed withand bonded to said coated particles.

2. A metal composition formed of particles of refractory metal selectedfrom the group consisting of tungsten and molybdenum, and a coatingthereon of metal selected from the group consisting of palladium,platinum and rhodium and metal selected from the first group of thePeriodic Table consisting of copper, silver and gold interspersed withand bonded to. said coated particles, said coated particles being formedof 99.99% to 10% of said refractory metal and .01% to of said coatingmetal, the coated particles forming 5 to 99% of said composition andsaid first group metal forming the balance.

3. An electric contact formed of a metal composition composed ofparticles of refractory metal selected from the group consisting oftungsten and molybdenum, and a coating on said par ticles of metalselected from the group consisting of palladium, platinum and rhodiumand metal selected from the first group of the Periodic Table consistingof copper, silver and gold interspersed with and bonded to said coatedparticles.

i. An electric contact formed of a metal com position composed ofparticles of refractory metal selected from the group consisting oftungsten and molybdenum, and a coating on said particles of metalselected from the group consisting of palladium, platinum and rhodiumand metal selected from the first group of the Periodic Table consistingof copper, silver and gold interspersed with and bonded to said coatedparticles, said coated particles being formed of 99.99% to 10% of saidrefractory metal and .01 to 90% of said coating metal, the coatedparticles forming 5 to 99% of said composition and said first groupmetal forming the balance.

FRANZ R. HENSEL. EARL I. LARSEN.

